The present invention concerns a system for the automatic braking of an elevator car designed to stop it when it reaches or exceeds a limit speed of movement within a lift shaft.
Such automatic braking systems are already known which generally consist of a stop mechanism comprising a stop pulley designed to be driven in rotation at the same time as said car moves. Said stop pulley is designed to rotate freely when its speed of rotation is less than a threshold speed of rotation and to lock when its speed of rotation is equal to or greater than said threshold speed of rotation. They also comprise a mechanism for controlling the action of said brakes when said stop pulley is locked.
FIG. 1 shows an elevator installation equipped with a braking system according to the known state of the art. This installation consists essentially of an elevator car 10 which is moved between the different floors of an elevator shaft (not shown), for example by means of a machinery 20 acting on a cable or a cluster of traction cables 21 and having a counterweight 22. The elevator car 10 is guided in its movement by lateral rails extending vertically in the elevator shaft and on which the car 10 bears through guides 31. For reasons of clarity, only one of these rails 30 has been depicted in FIG. 1.
The elevator car 10 has a control mechanism 11 provided for controlling the action of the brakes 10 and 13 depicted here schematically in the form of simple wedges, The brakes 12 and 13 act generally on the rails 30 of the elevator car 10. These brakes 12 and 13 are also known in the art as "safety stop clamps". They act one in one direction of movement of the car 10, the other in the other direction.
As for the automatic braking system, this includes a stop pulley 50 which is mounted on the masonry in the top part of the elevator shaft and an endless cable 60 wound between the stop pulley 50 and a return pulley 51. The endless cable 60 is tensioned by means of a tension weight 52 acting on the return pulley 51.
A control mechanism 53 is fixed on the one hand to the endless cable 60 and on the other hand to the car 53. In normal operation, that is to say when the speed of movement of the car 10 is less than a limit speed, the car 10 drives the cable 60. The mechanism 53 is not stressed and therefore does not act on the control mechanism 11 of the brakes 12 and 13.
On the other hand, when the speed of the car 10 reaches or exceeds a limit speed, the stop pulley 50 locks and the cable 60 is immobilised. The mechanism 53 is stressed since it is on the one hand immobilised by the cable 60 and on the other hand fixed to the car 10, which is still moving. The effect of this stressing of the mechanism 53 is to actuate the control mechanism 11, which then acts on the brakes 12 and 13. These in return act on the rails 30, which has the effect of immobilising the car 10.
One of the drawbacks of the braking system of the state of the art presented above is its relatively large bulk because notably of the use of an endless cable, which has two parallel lengths for which it is necessary to reserve space in the elevator shaft.
The other drawback of this braking system lies in the fact that the stop pulley is necessarily mounted in the top part of the elevator shaft, generally on the same piece of masonry as that on which the drive motor 20 rests. The risks of accident related to this piece are therefore not covered by the braking system.